This invention relates generally to gas turbine engines and more particularly to bearings used in such engines.
A turbofan gas turbine engine used for powering an aircraft in flight typically includes, in serial, axial flow relationship, a fan, a low pressure compressor or booster, a high pressure compressor, a combustor, a high pressure turbine, and a low pressure turbine. The combustor generates combustion gases that are channeled in succession to the high pressure turbine where they are expanded to drive the high pressure turbine, and then to the low pressure turbine where they are further expanded to drive the low pressure turbine. The high pressure turbine is drivingly connected to the high pressure compressor via a first rotor shaft, and the low pressure turbine is drivingly connected to both the fan and the booster via a second rotor shaft.
The rotating parts of the engine are supported by a number of bearings that must be suitably lubricated during operation. A typical lubricating system includes an oil tank holding lubricating oil that is pumped to the various bearings for the lubrication thereof. Oil discharged from the bearings is collected in suitable sumps and is commonly referred to as scavenge oil. The scavenge oil is pumped back to the oil tank from where it repeats the lubricating circuit.
The bearings, which are exposed to high temperature, high RPM operation, are subject to failure over time. As a bearing begins to fail, metallic chips break off and are released to the oil sump where they become entrained in the scavenge oil. Accordingly, lubricating systems typically include magnetic chip detectors that detect the increased presence of metallic chips in the scavenge oil, thereby indicating the onset of bearing failure. This allows the bearings to be replaced before complete failure occurs.
One current bearing design includes a bearing race concentrically mounted on the shaft. A retainer nut is threaded onto the end of the shaft for retaining an oil sump seal on the shaft. A separate spacer is located between the retainer nut and the bearing race for facilitating assembly of the bearing. Centrifugal forces cause many of the metallic chips in the scavenge oil to migrate underneath the spacer where they become trapped at the retainer nut. The oil flowing through the sump cannot overcome the viscous and centrifugal forces holding the metallic chips against the metal rotating parts. Thus, the migration of chips from a failing bearing to the magnetic chip detector, which is normally disposed in the scavenge oil pump, upstream of the oil filter, is limited because a large quantity of chips get trapped by the retainer nut and spacer. The reduced amount of chips reaching the magnetic chip detector means that impending bearing failures are not reliably detected.
Accordingly, there is a need for bearing design in which the metallic chips do not become trapped and prevented from reaching the magnetic chip detector.
The above-mentioned need is met by the present invention, which provides a retainer nut for use in a bearing assembly disposed between a shaft and another structural element. The bearing assembly includes a first race mounted to the shaft, a second race mounted to the structural element, and a plurality of bearing elements disposed between the first and second races. The retainer nut is attached to the shaft and includes a cylindrical ring portion and an annular flange disposed on one end of the ring portion. The flange extends radially inward from the ring portion, and a plurality of openings is formed through the flange.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.